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NATIONAL
NCHRP REPORT 669
COOPERATIVE
HIGHWAY
RESEARCH
PROGRAM
Models for Predicting
Reflection Cracking of
Hot-Mix Asphalt Overlays
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TRANSPORTATION RESEARCH BOARD 2010 EXECUTIVE COMMITTEE*
OFFICERS
CHAIR: Michael R. Morris, Director of Transportation, North Central Texas Council of Governments, Arlington
VICE CHAIR: Neil J. Pedersen, Administrator, Maryland State Highway Administration, Baltimore
EXECUTIVE DIRECTOR: Robert E. Skinner, Jr., Transportation Research Board
MEMBERS
J. Barry Barker, Executive Director, Transit Authority of River City, Louisville, KY
Allen D. Biehler, Secretary, Pennsylvania DOT, Harrisburg
Larry L. Brown, Sr., Executive Director, Mississippi DOT, Jackson
Deborah H. Butler, Executive Vice President, Planning, and CIO, Norfolk Southern Corporation, Norfolk, VA
William A.V. Clark, Professor, Department of Geography, University of California, Los Angeles
Eugene A. Conti, Jr., Secretary of Transportation, North Carolina DOT, Raleigh
Nicholas J. Garber, Henry L. Kinnier Professor, Department of Civil Engineering, and Director, Center for Transportation Studies, University of
Virginia, Charlottesville
Jeffrey W. Hamiel, Executive Director, Metropolitan Airports Commission, Minneapolis, MN
Paula J. Hammond, Secretary, Washington State DOT, Olympia
Edward A. (Ned) Helme, President, Center for Clean Air Policy, Washington, DC
Adib K. Kanafani, Cahill Professor of Civil Engineering, University of California, Berkeley
Susan Martinovich, Director, Nevada DOT, Carson City
Debra L. Miller, Secretary, Kansas DOT, Topeka
Sandra Rosenbloom, Professor of Planning, University of Arizona, Tucson
Tracy L. Rosser, Vice President, Corporate Traffic, Wal-Mart Stores, Inc., Mandeville, LA
Steven T. Scalzo, Chief Operating Officer, Marine Resources Group, Seattle, WA
Henry G. (Gerry) Schwartz, Jr., Chairman (retired), Jacobs/Sverdrup Civil, Inc., St. Louis, MO
Beverly A. Scott, General Manager and Chief Executive Officer, Metropolitan Atlanta Rapid Transit Authority, Atlanta, GA
David Seltzer, Principal, Mercator Advisors LLC, Philadelphia, PA
Daniel Sperling, Professor of Civil Engineering and Environmental Science and Policy; Director, Institute of Transportation Studies; and Interim
Director, Energy Efficiency Center, University of California, Davis
Kirk T. Steudle, Director, Michigan DOT, Lansing
Douglas W. Stotlar, President and CEO, Con-Way, Inc., Ann Arbor, MI
C. Michael Walton, Ernest H. Cockrell Centennial Chair in Engineering, University of Texas, Austin
EX OFFICIO MEMBERS
Peter H. Appel, Administrator, Research and Innovative Technology Administration, U.S.DOT
J. Randolph Babbitt, Administrator, Federal Aviation Administration, U.S.DOT
Rebecca M. Brewster, President and COO, American Transportation Research Institute, Smyrna, GA
George Bugliarello, President Emeritus and University Professor, Polytechnic Institute of New York University, Brooklyn; Foreign Secretary,
National Academy of Engineering, Washington, DC
Anne S. Ferro, Administrator, Federal Motor Carrier Safety Administration, U.S.DOT
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Edward R. Hamberger, President and CEO, Association of American Railroads, Washington, DC
John C. Horsley, Executive Director, American Association of State Highway and Transportation Officials, Washington, DC
David T. Matsuda, Deputy Administrator, Maritime Administration, U.S.DOT
Victor M. Mendez, Administrator, Federal Highway Administration, U.S.DOT
William W. Millar, President, American Public Transportation Association, Washington, DC
Robert J. Papp (Adm., U.S. Coast Guard), Commandant, U.S. Coast Guard, U.S. Department of Homeland Security, Washington, DC
Cynthia L. Quarterman, Administrator, Pipeline and Hazardous Materials Safety Administration, U.S.DOT
Peter M. Rogoff, Administrator, Federal Transit Administration, U.S.DOT
David L. Strickland, Administrator, National Highway Traffic Safety Administration, U.S.DOT
Joseph C. Szabo, Administrator, Federal Railroad Administration, U.S.DOT
Polly Trottenberg, Assistant Secretary for Transportation Policy, U.S.DOT
Robert L. Van Antwerp (Lt. Gen., U.S. Army), Chief of Engineers and Commanding General, U.S. Army Corps of Engineers, Washington, DC
*Membership as of July 2010.
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NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM
NCHRP REPORT 669
Models for Predicting
Reflection Cracking of
Hot-Mix Asphalt Overlays
Robert L. Lytton
Fang Ling Tsai
Sang-Ick Lee
Rong Luo
Sheng Hu
Fujie Zhou
TEXAS TRANSPORTATION INSTITUTE
TEXAS A&M UNIVERSITY
College Station, TX
Subscriber Categories
Pavements
Research sponsored by the American Association of State Highway and Transportation Officials
in cooperation with the Federal Highway Administration
TRANSPORTATION RESEARCH BOARD
WASHINGTON, D.C.
2010
www.TRB.org
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NATIONAL COOPERATIVE HIGHWAY NCHRP REPORT 669
RESEARCH PROGRAM
Systematic, well-designed research provides the most effective Project 01-41
approach to the solution of many problems facing highway ISSN 0077-5614
administrators and engineers. Often, highway problems are of local ISBN 978-0-309-15505-2
interest and can best be studied by highway departments individually Library of Congress Control Number 2010936725
or in cooperation with their state universities and others. However, the © 2010 National Academy of Sciences. All rights reserved.
accelerating growth of highway transportation develops increasingly
complex problems of wide interest to highway authorities. These
problems are best studied through a coordinated program of COPYRIGHT INFORMATION
cooperative research.
Authors herein are responsible for the authenticity of their materials and for obtaining
In recognition of these needs, the highway administrators of the written permissions from publishers or persons who own the copyright to any previously
American Association of State Highway and Transportation Officials published or copyrighted material used herein.
initiated in 1962 an objective national highway research program Cooperative Research Programs (CRP) grants permission to reproduce material in this
employing modern scientific techniques. This program is supported on publication for classroom and not-for-profit purposes. Permission is given with the
understanding that none of the material will be used to imply TRB, AASHTO, FAA, FHWA,
a continuing basis by funds from participating member states of the
FMCSA, FTA, or Transit Development Corporation endorsement of a particular product,
Association and it receives the full cooperation and support of the method, or practice. It is expected that those reproducing the material in this document for
Federal Highway Administration, United States Department of educational and not-for-profit uses will give appropriate acknowledgment of the source of
any reprinted or reproduced material. For other uses of the material, request permission
Transportation.
from CRP.
The Transportation Research Board of the National Academies was
requested by the Association to administer the research program
because of the Board's recognized objectivity and understanding of
NOTICE
modern research practices. The Board is uniquely suited for this
purpose as it maintains an extensive committee structure from which The project that is the subject of this report was a part of the National Cooperative Highway
Research Program, conducted by the Transportation Research Board with the approval of
authorities on any highway transportation subject may be drawn; it the Governing Board of the National Research Council.
possesses avenues of communications and cooperation with federal,
The members of the technical panel selected to monitor this project and to review this
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relationship to the National Research Council is an insurance of The report was reviewed by the technical panel and accepted for publication according to
procedures established and overseen by the Transportation Research Board and approved
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by the Governing Board of the National Research Council.
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The opinions and conclusions expressed or implied in this report are those of the
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The program is developed on the basis of research needs identified Research Board, the National Research Council, or the program sponsors.
by chief administrators of the highway and transportation departments The Transportation Research Board of the National Academies, the National Research
and by committees of AASHTO. Each year, specific areas of research Council, and the sponsors of the National Cooperative Highway Research Program do not
needs to be included in the program are proposed to the National endorse products or manufacturers. Trade or manufacturers' names appear herein solely
because they are considered essential to the object of the report.
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The needs for highway research are many, and the National
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Printed in the United States of America
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COOPERATIVE RESEARCH PROGRAMS
CRP STAFF FOR NCHRP REPORT 669
Christopher W. Jenks, Director, Cooperative Research Programs
Crawford F. Jencks, Deputy Director, Cooperative Research Programs
Amir N. Hanna, Senior Program Officer
Eileen P. Delaney, Director of Publications
Margaret B. Hagood, Editor
NCHRP PROJECT 01-41 PANEL
Field of Design--Area of Pavements
Kevin D. Hall, University of Arkansas - Fayetteville, Fayetteville, AR (Chair)
Bruce A. Chadbourn, Minnesota DOT, Maplewood, MN
Dar-Hao Chen, Texas DOT, Austin, TX
Adam J. T. Hand, Granite Construction, Inc., Sparks, NV
Abdallah J. Jubran, Georgia DOT, Forest Park, GA
Linda M. Pierce, Applied Pavement Technology, Inc., Santa Fe, NM (formerly Washington State DOT)
Shakir R. Shatnawi, Shatec Engineering Consultants LLC, El Dorado Hills, CA (formerly California DOT)
Timothy E. Smith, Maryland State Highway Administration, Hanover, MD
Nelson H. Gibson, FHWA Liaison
Stephen F. Maher, TRB Liaison
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FOREWORD
By Amir N. Hanna
Staff Officer
Transportation Research Board
This report presents mechanistic-based models for predicting the extent and severity of
reflection cracking in hot-mix asphalt (HMA) overlays. These models were developed for
use in the design and analysis of HMA overlays; they can be incorporated into the AASHTO
Mechanistic-Empirical Pavement Design Guide (MEPDG) software. The report and accom-
panying software will guide pavement and construction engineers in identifying and spec-
ifying HMA overlays for asphalt and concrete pavements that will provide desired service
life and performance. The information contained in the report will be of immediate inter-
est to state pavement engineers and others concerned with the design and rehabilitation of
asphalt and concrete pavements.
Reflection cracking is one of the primary forms of distress in HMA overlays of flexible and
rigid pavements. In addition to affecting ride quality, the penetration of water and foreign
debris into these cracks accelerates the deterioration of the overlay and the underlying pave-
ment, thus reducing service life. The basic mechanism causing reflection cracking is strain
concentration in the overlay due to movement in the existing pavement in the vicinity of joints
and cracks. This movement may be induced by bending or shearing action resulting from traf-
fic loads or temperature changes and is influenced by traffic volume and characteristics, daily
and seasonal temperature variations, and other factors (e.g., pavement structure and condi-
tion, HMA mixture properties, the degree of load transfer at joints and cracks). Preliminary
models for predicting the extent and severity of reflection cracking in HMA overlays have been
developed; however, only limited research has been performed to evaluate and validate these
models. Thus, research was needed to address the issues associated with reflection cracking
and to develop mechanistic-based models that account for the effects of reflection cracking on
performance for use in mechanistic-empirical procedures for the analysis and design of HMA
overlays.
Under NCHRP Project 1-41, "Models for Predicting Reflection Cracking of Hot-Mix
Asphalt Overlays," Texas A&M Research Foundation of College Station, Texas worked with
the objective of identifying or developing mechanistic-based models for predicting reflection
cracking in HMA overlays of flexible and rigid pavements and associated computational soft-
ware for use in mechanistic-empirical procedures for overlay design and analysis. To accom-
plish this objective, the research reviewed available information relevant to reflection crack-
ing of HMA overlays, considered the factors that contribute to reflection cracking, evaluated
available models, and developed mechanistic-based models for predicting the extent and
severity of reflection cracking in HMA overlays. In addition, the research developed software,
compatible with the MEPDG software, to facilitate use of these models for (1) the design and
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analysis of HMA overlays or (2) developing calibration coefficients and enhanced models for
specific types of overlays and climatic conditions.
The models developed in this research will be particularly useful to highway agencies
because they allow consideration of reflection cracking in the design of HMA overlays and
selection of overlays for asphalt and concrete pavements that are expected to yield economic
and other benefits. The incorporation of these models into the AASHTO MEPDG will help
account for the effects of reflection cracking on performance thus improving the analysis
and design of HMA overlays of flexible and rigid pavements.
Appendixes A through T contained in the research agency's final report provide detailed
information on the different aspects of the research, including user guides to support the
software. These appendixes are not published herein but they are available on the NCHRP
Report 669 summary web page at http://www.trb.org/Main/Blurbs/163988.aspx.
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CONTENTS
1 Chapter 1 Introduction and Research Approach
1 Introduction
1 Objective
1 Scope
1 Organization of the Report
2 Research Approach
2 Material Properties
3 Traffic
3 Crack Growth and Pavement Temperature
3 Computational Efficiency
3 Calibration to Field Data
4 Use in Design
5 Chapter 2 Findings
5 Introduction
5 Reflection Cracking Definition and Mechanisms
5 Available Reflection Cracking Models
6 Selection of a Reflection Cracking Model
7 Process of Constructing a Calibrated Reflection Cracking Model
8 Overlay Sections with Sufficient Data for Model Development
8 Collection of Pavement Structure Data
10 Pavement Distress Data Collection
10 Traffic Data Collection
11 Categorization of Traffic Loads
11 Classification of Vehicles
11 Axle Load Distribution Factor
13 Categorizing Traffic Load
14 Climatic Data Collection
14 Finite Element Method for Calculating SIF
17 Method of Predicting SIF
19 Traffic Loads and Tire Footprints
19 Tire Patch Length
19 Determination of the Effect of Cumulative Axle Load
Distribution on Tire Length
19 Modeling of Cumulative Axle Load Distribution
20 Determination of Hourly Number of Axles
20 Probability Density on Tire Patch Length
26 Reflection Cracking Amount and Severity Model
27 Calibration of Field Reflection Cracking Model
28 System Identification Process
29 Parameter Adjustment and Adaption Algorithm
30 Calibrating Reflection Cracking Model of Test Sections
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33 Prediction of Temperature in a HMA Overlay
33 Heat Transfer in Pavement
34 The Surface Boundary Condition
34 The Bottom Boundary Condition
35 Numerical Solution of the Model
35 Obtaining Hourly Climatic Input Data
35 Stiffness, Tensile Strength, Compliance, and Fracture Properties of Mixtures
36 Artificial Neural Network Algorithms for Witczak's Complex
Modulus Models
38 Models of Tensile Strength of Mixtures
38 Models of Paris and Erdogan's Law Fracture Coefficients A and n
39 Healing Coefficients
39 Stress Wave Pattern Correction for Viscoelastic Crack Growth
39 Computational Method for Crack Growth Due to Traffic
41 Computational Method for Viscoelastic Thermal Stresses
42 Supervisory Program to Compute Crack Growth
42 User Interface Program for Input and Output Data
42 Computation-to-Field Calibration Coefficients
44 Validation of the Calibration Coefficients
48 Chapter 3 Interpretations, Appraisal, and Applications
48 Introduction
48 The Model Development Process
48 Mechanistic Prediction of Crack Growth
49 HMA Overlay Material Properties
49 Weather Data and Temperature Prediction
49 Consistent Description of Reflection Cracking Distress
49 Calibration of Calculated Overlay Life to the Observed Distress
50 Calibrated Results Compared with Observed Field Data
50 Calibration Coefficients by Regression Analysis
50 Predictions of Overlay Reflection Cracking
55 Calibration of the Computational Model to Field Data
56 Chapter 4 Summary and Suggested Research
56 Summary
56 Suggested Research
58 References
60 Appendices
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AUTHOR ACKNOWLEDGMENTS
The research reported herein was performed under NCHRP Project 1-41 by the Texas Transportation
Institute of the Texas A&M University. Robert L. Lytton, Professor of Civil Engineering, was the princi-
pal investigator and the co-principal investigator was Fujie Zhou, Research Engineer. The other authors
of this report are Fang Ling Tsai and Sang-Ick Lee, both Research Assistants and Sheng Hu and Rong Luo,
both Post-Doctoral Research Associates.
The research work was materially aided by the assistance given by Jagannath Mallela and Harold L. von
Quintus of the Applied Research Associates, Inc. (ARA), who provided information and data on the New
York City overlay test sections. Permission to use that data was given by the City of New York, Depart-
ment of Design and Construction, Division of Infrastructure. The Texas overlay test section data used in
the project were provided by Joe W. Button and Arif Chowdhury of the Texas Transportation Institute
with the approval of German Claros, Research Coordinator with the Texas Department of Transporta-
tion. The extraction of data and categorization of overlay sections from the Long-Term Pavement Per-
formance database was done by Thomas Freeman of the Texas Transportation Institute. The two pro-
grams produced in the project are written in the C# language as was suggested by Gregg Larson of ARA
and supported by Vicki Schofield of AASHTO. All subprograms which were not originally in that lan-
guage were re-written by Sheng Hu of the Texas Transportation Institute. The Artificial Neural Network
models of the mixture moduli and the stress intensity factors were provided under a subcontract by Halil
Ceylan of Iowa State University. Helpful advice and direction on the use of weather databases was given
by Gregg Larson of ARA. The temperature prediction model used in both the design and calibration pro-
grams and its description was provided by Charles J. Glover, Professor of Chemical Engineering, Texas
A&M University and by Research Assistants Rongbin Han and Xin Jin, both of the Chemical Engineer-
ing Department of Texas A&M University. The thermal stress prediction program was provided by Rey-
naldo Roque of the University of Florida in Gainesville. The finite element program which generated the
stress intensity factors which were modeled with the Artificial Neural Network algorithms was written by
Sheng Hu, description of that model was written by Sheng Hu, Xiaodi Hu, and Lubinda Walubita, all
Post-Doctoral Research Associates and by Fujie Zhou, Research Engineer with the Texas Transportation
Institute. The review and evaluation of available reflection cracking models was written by Fujie Zhou.
Cathy Bryan of the Texas Transportation Institute was responsible for the final manuscript preparation.
